1. Field of the Invention
The present invention relates to a resist cover film-forming material which can be suitably used for a resist cover film for liquid immersion exposure to protect a resist film from a fluid used in a liquid immersion exposure technique in which improvements in resolution can be realized by filling with a medium (a fluid) having a refractive index “n” greater than 1 (the refractive index of air) between a projector lens of an exposure device and a wafer, and can transmit ArF excimer laser lights, and the like. The present invention also relates to a process for forming a resist pattern, a semiconductor device, and a process for manufacturing the same.
2. Description of the Related Art
In recent years, semiconductor integrated circuits are becoming more highly integrated. Accompanying this trend, the smallest patterns extend to regions of 100 nm or less. In order to form fine patterns, a method is conventionally used in which a surface of a workpiece to be processed on which a thin film is formed, is coated by a resist film, is selectively exposed, and thereafter, is developed to thereby form a resist pattern, and then dry etching is carried out by using the resist pattern as a mask, and thereafter, by removing the resist pattern, the desired pattern is obtained.
In order to form a further finer pattern, it is necessary to make the light source of the exposure device be a short wavelength, as well as to develop resist materials which have high resolution suitable for the characteristics of the light source. However, in order to make a light source of an exposure device be a short wavelength, it is necessary to improve the exposure device, which results in very high costs. As future exposure light that can replace KrF (krypton fluoride) excimer laser light of wavelength 248 nm which has been used so far, ArF excimer laser lights of wavelength 193 nm are progressively put into practical use, and exposure devices having ArF excimer laser light are begun to be commercially available. However, exposure devices having ArF excimer laser light are still rather expensive. In addition, the development of new resist materials suitable for exposure with the use of light of short wavelength is not easy. A resist material which is effective in exposure with light of short wavelength has not yet been proposed. For the reason, it is difficult to realize a formation of a fine pattern by using conventional processes for forming a resist pattern.
Then, as a latest exposure technique, a liquid immersion exposure technique has become a focus of attention. According to the liquid immersion exposure technique, by filling with a medium (a fluid) having a refractive index “n” greater than 1 (the refractive index of air) between a projector lens of an exposure device and a wafer, it is possible to realize improvements in resolution of a resist material. Typically, the resolution of the exposure device is calculated by the equation, Resolution (R)=k(coefficient)×λ(wavelength of light source)/NA(numerical aperture), and the shorter the wavelength λ of the light source and the greater the numerical aperture (NA) of the projector lens, the higher the resolution can be obtained. In the equation, the numerical aperture NA is expressed by the equation, NA =n×sin α, where “n” represents a refractive index of a medium through which the exposure light is passing, and “α” represents an angle formed by the exposure light. In conventional processes for forming a pattern, exposure is carried out in the atmosphere, and so the refractive index “n” is 1. However, in the liquid immersion exposure technique, a fluid having a refractive index “n” greater than 1 is used and filled in between the projector lens and the wafer. Thus, in the equation of the numerical aperture NA, the value “n” is increased, and in the angle of incidence “α” of the same exposure light, the minimum resolution can be reduced to 1/n. Further, in the same numerical aperture NA, the angle of incidence “α” can be reduced, and the focus depth can be multiplied to n times.
Such a liquid immersion technique using a fluid having a refractive index greater than that of air is the already-existing technique in the area of microscope. However, for an application of the technique into fine processing technique, there is only a limited proposal of an exposure device which carries out exposure by filling with a fluid having a refractive index slightly lower than that of the lens (see Japanese Patent Application Laid-Open OP-A) No. 62-065326). For the practical use of such an exposure device, it has begun to be considered just over the last few years. Problems with liquid immersion exposure devices and resist materials used for the liquid immersion exposure devices become gradually revealed.
One of the problems, for example, is that since a resist film is exposed to a fluid (for example, water) filled between the projector lens and the wafer, and acid components generated in the resist film during the exposure are exuded into water, resulting in degradation of the sensitivity of the resist. When excimer laser light is applied to the resist film in a condition where water infiltrates in the resist film, a chemical reaction that does not occur in the conventional dry atmosphere occurs, which causes impairment of the intrinsic performance of the resist, and eluted materials contaminate the projector lens or the like of the exposure device. The contamination of eluted materials causes defects in exposure, and degradation of resolution.
In order to prevent these problems, a process for forming a resist cover film on the top surface of the resist layer is studied, however, it is difficult to form a resist cover film to the top surface of the resist film by a resist cover film without dissolving the resist film and without mixing with the resist film. In addition, since the ArF excimer laser light has a short wavelength of 193 nm and is not transmissive to typical organic matters, the range of selection of materials usable for resist cover films is extremely narrow.
As a cover film that is not based on the assumption of a liquid immersion exposure technique, a cover film using amorphous polyolefin has been proposed (see Japanese Patent Application Laid-Open UP-A) No. 06-95397). According to the disclosure, when an ArF resist which differs in composition of a resin from that of KrF resist is used, the cover film formed by using the ArF resist has insufficient film-forming properties, and the coverage is poor when a thin film is formed with the ArF resist.
On the other hand, a resist coating composition has been proposed for the purpose of improving its coating property (see Japanese patent Application Laid-Open No. 2002-296787). The resist coating composition, however, contains aromatic ester or ether, and thus the transparency thereof is low, and it is impossible to use ArF excimer laser lights.
In addition, as a cover film used in a liquid immersion exposure technique, a cover film using an alkali soluble fluorinated alicyclic resin has been proposed (see Japanese Patent Application Laid Open (JP-A) No. 2005-157259), however, because the polarity of the cover film is high, the cover film is mixed with the ArF resist at the surface region, which causes degradation of form of pattern; and polar additives such as an acid generator and a quencher used in the resist diffuse to the cover film, infiltrate to the cover film to thereby contaminate the fluid used for liquid immersion exposure.
Accordingly, the current situation is that there has not yet been developed a material which is usable for a resist cover film for liquid immersion exposure and is capable of forming a resist film without diffusing the resist film, efficiently protecting the resist film from the fluid having a high-refractive index without impairing the intrinsic resist performance, having a high-transmittance to the ArF excimer laser light, and causing an extremely little amount of contaminant eluted from the resist film to the fluid having a high-refractive index. The related techniques using such a material have also not yet been developed. Therefore, it is desired that such technique to be developed.
The object of the present invention is to overcome the above-mentioned conventional problems and to achieve the following objects.
Namely, an object of the present invention is to provide a resist cover film-forming material which can be suitably used for liquid immersion exposure to protect from the fluid in a liquid immersion exposure technique that realizes improvements in resolution by filling with a medium (a fluid) having a refractive index “n” greater than 1 (the refractive index of air) between a projector lens of an exposure device and a wafer and can transmit ArF excimer laser lights, and the like.
Another object of the present invention is to provide a process for forming a resist pattern which can efficiently protect the resist film from the fluid, precisely carrying out exposure by liquid immersion exposure without impairing the function of the resist film, and forming a fine and highly precise resist pattern with ease and efficiency.
According to embodiments of the present invention, it is possible to form a fine and highly precise resist pattern by liquid immersion exposure without impairing the function of the resist film. Yet another object of the present invention is to provide a process for manufacturing a semiconductor device in which high-performance semiconductor devices having fine interconnection patterns formed by using the resist pattern can be efficiently mass produced, and is to provide a high-performance semiconductor which is manufactured by the process for manufacturing a semiconductor device and has fine interconnection patterns.
In view of the above-mentioned problems, inventors of the present invention have investigated enthusiastically, and have found the following findings. Specifically, when a composition which is nonphotosensitive (incapable of pattern forming) and contains a resin having an alicyclic skeleton at any of the main chain and the side chains is used as a resist cover film-forming material in a liquid immersion exposure technique, it is possible to form a resist cover film on a resist film as well as to obtain a resist cover film which is capable of efficiently protecting resist film from a fluid having a high-refractive index filled in between a projector lens and a wafer and is capable of transmitting ArF excimer laser lights and the like.